docs: def _getsie(self):
          """Return data as signed interleaved exponential-Golomb code.
  
          Raises InterpretError if bitstring is not a single exponential-Golomb code.
  
          """
          try:
              value, newpos = self._readsie(0)
              if value is None or newpos != self.len:
                  raise ReadError
          except ReadError:
              raise InterpretError("Bitstring is not a single interleaved exponential-Golomb code.")
          return value